Historical:Fairplay Member

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Handbook of Illinois Stratigraphy
Series Bulletin 95
Author H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date 1975
Link Web page
PDF PDF file
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Lithostratigraphy: Ottawa Limestone Megagroup >>Galena Group >>Kimmswick Subgroup >>Dunleith Formation >>Fairplay Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence


H. B. Willman and T. C. Buschbach

Name Origin

The Fairplay Member of the Dunleith Formation (Templeton and Willman, 1963, p. 121) overlies the Eagle Point Member, and is named for the town of Fairplay, Grant County, Wisconsin, 6 miles northeast of the type section.

Type Section

The type section of the Fairplay Member is part of the Dunleith Formation type section (in an exposure in the Mississippi River bluffs on the north side of East Dubuque (SE 19, 29N-2W)), where the Fairplay Member is 19.8 feet thick.

Extent and Thickness

The Fairplay Member is commonly 14-20 feet thick.


In the type section the Fairplay consists of relatively pure, lithographic limestone and is the top of the northern limestone facies. It is largely free of chert, but scattered nodules appear locally. The upper 1-3 feet is persistently argillaceous or shaly. These characteristics extend into the northern dolomite facies, but the member is not differentiated in the southern limestone facies.


Receptaculites oweni is common in many beds of the Fairplay Member, and the Fairplay is the Lower Receptaculites Zone.


TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation